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100 lines
2.1 KiB
Go
100 lines
2.1 KiB
Go
package main
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import (
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// "bufio"
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"fmt"
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"io"
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"os"
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)
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type CopyOp struct {
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Bytes int64
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Original, Backup *os.File
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}
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func copy(src, dst string) (CopyOp, error) {
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var co CopyOp
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sourceFileStat, err := os.Stat(src)
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if err != nil {
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return co, err
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}
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if !sourceFileStat.Mode().IsRegular() {
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return co, fmt.Errorf("%s is not a regular file", src)
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}
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source, err := os.Open(src)
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if err != nil {
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return co, err
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}
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co.Original = source
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defer source.Close()
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destination, err := os.Create(dst)
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if err != nil {
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return co, err
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}
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defer destination.Close()
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co.Backup = destination
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nBytes, err := io.Copy(destination, source)
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co.Bytes = nBytes
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return co, err
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}
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func restoreBackup(fn string) error {
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err := os.Remove(fn)
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if err != nil {
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// removing the original has failed.
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return fmt.Errorf("error removing modified file[%s] : %w", fn, err)
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}
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// copy the backup back to the original
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_, err = copy(fn+".bak", fn)
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if err != nil {
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return fmt.Errorf("error copying backup into original location[%s]: %w", fn, err)
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}
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// remove the backup
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err = os.Remove(fn + ".bak")
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if err != nil {
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// removing the backup has failed.
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return fmt.Errorf("error removing backup file[%s] : %w", fn+".bak", err)
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}
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return nil
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}
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// Update modifies the contents of a file in-place.
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func Update(fn string, newContents io.Reader) error {
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// create a backup copy
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copyOp, err := copy(fn, fn+".bak")
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if err != nil {
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return fmt.Errorf("error backing up file[%s]: %w", fn, err)
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}
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// truncate the original
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err = os.Truncate(fn, 0)
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if err != nil {
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err := restoreBackup(fn)
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if err != nil {
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return fmt.Errorf("error restoring backup: %w", err)
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}
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return fmt.Errorf("error truncating original file[%s]: %w", fn, err)
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}
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// copy new contents into original
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_, err = io.Copy(copyOp.Original, newContents)
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if err != nil {
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// the copy has failed. we need to remove the original
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err := restoreBackup(fn)
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if err != nil {
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return fmt.Errorf("error restoring backup: %w", err)
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}
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return fmt.Errorf("error writing new contents to file[%s] : %w", fn, err)
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}
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return nil
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}
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